Estimation Rounding

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Rounding to nearest 1, 10, 100, 1000 etc | Rounding to decimal places | Rounding to significant figures | Estimation

Rounding to nearest 1, 10, 100, 1000 etc


Remember the rule: ’Five or more’. Look at the next digit after the one to which you are correcting. If this is 5 or more, the digit before goes up.
To the nearest 10:
  • 34 becomes 30
  • 37 becomes 40

To the nearest 100:
  • 347 becomes 300
  • 357 becomes 400

To the nearest whole number

  • 86.4 becomes 86
  • 86.6 becomes 87

Rounding to decimal places

Use the ’Five or more’ rule to round to the appropriate number of decimal places in the same way for to the nearest whole number, 10, 100, etc.
The answer muse contain the number of decimal places that the rounding requires i.e. if rounded to 2 d.p. then answer must contain two digits after the decimal point even if this digits are 0s.

To 1 decimal place:
5.34 becomes 45.3 1 d.p.
45.39 becomes 45.4 1 d.p.

To 2 decimal places
45.392 becomes 45.39 2 d.p.
45.385 becomes 45.39 2 d.p.
45.395 becomes 45.40 2 d.p.

13.99 = 14.0 (1 d.p.)
0.905 = 0.91 (2 d.p.)
0.0076289 = 0.00763 (3 d.p.)

Rounding to significant figures

Usually, the digits in a number, not counting noughts at the beginning are significant figures. Identify the first significant figure. Use the ’Five or more’ rule to round.
Please note, leading and trailing zeros which are merely placeholders to indicate the scale of the number and are NOT significant. However, zeroes may need to be added to the answer to adjust the number to make it the correct size.

681 has 3 s.f. = 700 (1 s.f).39784 has 5 s.f. = 40000 (1 s.f.)
13.06 has 4 s.f. = 10 (1 s.f.)

In the following 2 roundings, the 0s after the nine and before the 76 are NOT significant, but must be added to the answer 0.008 in order to adjust the answer to the appropriate size.
0.900 = 0.9 (1 s.f.)
0.0076 = 0.008 (1 s.f.)

Rounding to nearest 1, 10, 100, 1000 etc | Rounding to decimal places | Rounding to significant figures | Estimation

Estimation


Rounding to nearest 1, 10, 100, 1000 etc | Rounding to decimal places | Rounding to significant figures | Estimation